Friday, December 3, 2010

Paper: Arctic changes not unprecedented; AGW 'does not stand out'

An article posted this week on the NIPPC website explains that according to computer models, signs of AGW (human-induced warming) should be most apparent at the poles, but a comprehensive review finds there is not 'unprecedented' warming or clear signs of AGW:

A long succession of climate models has consistently suggested that anthropogenic-induced global warming should be significantly amplified in earth's polar regions and, therefore, that the first signs of man's expected impact on the world's weather should be manifest in that part of the planet; or as Donella Meadows (2001) has described it, "the place to watch for global warming -- the sensitive point, the canary in the coal mine -- is the Arctic." So what have those who have looked for human-induced warming in the Arctic have found there?

One of the most recent and substantial of such efforts is the paper of White et al. (2010), who produced a comprehensive review -- and thoughtful analysis -- of past climate change in earth's north polar region, which was published in Quaternary Science Reviews.

In comparing the vast array of past climate changes in the Arctic with what the IPCC claims to be the "unprecedented" anthropogenic-induced warming of the past several decades, White et al. conclude that "thus far, human influence does not stand out relative to other, natural causes of climate change." In fact, they state that the data "clearly show" that "strong natural variability has been characteristic of the Arctic at all time scales considered," and they reiterate that the data suggest "that the human influence on rate and size of climate change thus far does not stand out strongly from other causes of climate change."

The nine researchers begin by describing how "processes linked with continental drift have affected atmospheric circulation, ocean currents, and the composition of the atmosphere over tens of millions of years," and that "a global cooling trend over the last 60 million years has altered conditions near sea level in the Arctic from ice-free year-round to completely ice covered." They also report that "variations in arctic insolation over tens of thousands of years in response to orbital forcing have caused regular cycles of warming and cooling that were roughly half the size of the continental-drift-linked changes," and that, in turn, this glacial-interglacial cycling "was punctuated by abrupt millennial oscillations, which near the North Atlantic were roughly half as large as the glacial-interglacial cycles." Last of all, they note that "the current interglacial, the Holocene, has been influenced by brief cooling events from single volcanic eruptions, slower but longer lasting changes from random fluctuations in the frequency of volcanic eruptions, from weak solar variability, and perhaps by other classes of events."

3 comments:

they say... "The data clearly show that strong natural variability has been characteristic of the Arctic at all time scales considered. The data suggest the twin hypotheses that the human influence on rate and size of climate change thus far does not stand out strongly from other causes of climate change, but that projected human changes in the future may do so."